1. Field of the Invention
The invention relates to a process for the continuous preparation of aqueous synthetic resin dispersions in a tubular reactor.
2. Description of the Prior Art
There are numerous processes for continuous emulsion polymerization. They are carried out mostly in agitator vessels subject to continuous flow, which--as in the batch process--are normally made of steel and are sometimes lined with enamel. Tubular reactors for continuous emulsion polymerization have also been described. They provide a shorter retention time and thus a narrower particle size distribution and allow greater heat dissipation due to the more favorable surface-to-volume ratio.
FR No. 842 829 (1938) describes a continuous emulsion polymerization in a coiled tube measuring 60 m in length and 25 mm in diameter. Steel and glass are suggested as materials for this tube. In FR No. 847 151 the material making up the tube for a similar polymerization apparatus is not mentioned at all. M. Gosh and T. H. Forsyth (ACS Symposium Series 24 "Emulsion Polymerization") used a coiled tube made of steel measuring 73 m in length and 1.27 cm in diameter in scientific experiments on the continuous emulsion polymerization of styrene.
These simple tubular reactors have not found industrial applications because the danger of obstructions due to attachments to the tube wall must always be considered. As the location of an obstruction in a steel tube cannot be determined from the outside, and the obstruction is difficult to remove, the entire tubular reactor often fails due to a small obstruction.
There has been no lack of efforts to eliminate obstructions in continuous emulsion polymerization in tubular reactors through the installation of mixers and the like. In FR No. 843 845 such a tubular reactor measuring 3.4 m in length and 12 cm in diameter with a mixer passing through the length of the reactor was described. However, the material making up the tube and mixer is not mentioned. A similar tubular reactor, enameled on the inside, is described in DE No. 880 938. In the tubular reactor according to DE No. 1 137 216, in addition to the mixer, a movable scraper is provided along the longitudinal axis of the tube, which removes attachments from the mixer and tube wall. Here, too, the material is not mentioned.
Therefore, a need continues to exist for a process whereby continuous emulsion polymerizations may be conducted in a tubular reactor with minimal risk of obstruction. Such obstructions continue to plague industry with large losses in plant investments.